Flow measuring devices are widely used, especially in process measurements technology. By way of example, magneto-inductive, flow measuring devices utilize for volumetric flow measurement the principle of electrodynamic induction and are described in a large number of publications. Charge carriers of the medium moved perpendicularly to a magnetic field induce a measurement voltage in measuring electrodes arranged essentially perpendicularly to the flow direction of the medium and perpendicularly to the direction of the magnetic field. The measurement voltage induced in the measuring electrodes is proportional to the flow velocity of the medium averaged over the cross section of the measuring tube and is thus proportional to the volume flow rate. If the density of the medium is known, the mass flow in the pipeline, or in the measuring tube, can be determined. The measurement voltage is usually sensed via a measuring electrode pair, which is arranged in the direction of the measuring tube axis at the region of maximum magnetic field strength and where, thus, the maximum measurement voltage is to be expected.
Magneto-inductive, flow measuring devices include, in such case, usually a measuring tube of metal, lined with a liner of polymer. In addition, there are also magneto-inductive, flow measuring devices with measuring tubes of synthetic material, e.g. plastic. This can have the disadvantage of a greater, and possibly even partially plastic, deformation in the case of the exceeding of a certain pressure of the medium in the measuring tube or after a large number of pressure cycles.
Offenlegungsschrift DE 103 47 890 A1 discloses a magneto-inductive, flow measuring device having a measuring tube composed of layers of fiber composite materials. Between the measuring tube interior and the measuring tube exterior, a strain gage is embedded in the layers, in order to monitor the permitted loading in the particular installation. This does not have a direct influence on the measuring of the flow.